Application analysis of Android handler main thread and general threading communication

handler definition: mainly accepts the data sent by the child thread, and updates the UI with this data in conjunction with the main thread .
Explanation: When the application starts,Android first turns on a main thread (that is, the UI thread), the main thread is the UI control in the management interface , for event distribution, for example, if you click on a button, Android will distribute the event to the button, To respond to your actions. If you need a time-consuming operation at this time, for example: network read data, or read a large local file, you can not put these operations in the main thread, if you put in the main thread, the interface will appear suspended animation, if 5 seconds has not been completed, you will receive an Android system error message Force Close. This time we need to put these time-consuming operations on a sub-thread, because the child threads involve UI updates, the Android main thread is not secure, that is, the update UI can only be updated in the main thread, and the operations in the child threads are dangerous. At this time, handler appeared to solve this complex problem. Since handler runs in the mainline approached (UI thread), it and the child thread can pass the data through the message object, and at this time, the handler is assumed to be transmitted by the receiving sub-thread (the child thread is passed with the Sedmessage () method) Message object, ( Contains data), put these messages into the main thread queue, with the main thread to update the UI.

Handler some features
Handler can distribute the Message object and the Runnable object into the main thread, and each handler instance is bound to create his line approached (typically on the main thread).
It has two functions: (1), arranges messages or runnable to be executed somewhere in a main thread, and (2) arranges an action to execute on a different thread.

Some ways to distribute messages in handler
Post (Runnable)
Postattime (Runnable,long)
Postdelayed (Runnable Long)
Sendemptymessage (int)
SendMessage (Message)
Sendmessageattime (Message,long)
Sendmessagedelayed (Message,long)
The Post class method above allows you to arrange a runnable object into the main thread queue,
The SendMessage class method allows you to schedule a message object with data to queue and wait for updates.

To change the UI content only within the main thread, here is an implementation on Android that dynamically changes the content of the UI interface: Start a thread timer, which is responsible for the specific action of dynamic changes to the UI, and then define a thread that is responsible for the communication between the main thread and the timer thread. This thread is Handler! It's runnable and activity.

Application analysis of Android handler main thread and general threading communication